The issue of climate change has become highly important over the last decades. All sectors need to find solutions in order to reduce the carbon footprint and the built environment sector is definitely not an exception to this. One of the solutions is to use more biobased materials, such as timber. The use in timber is not only limited to low-rise buildings, more mid- and high-rise buildings are being built as well. The number of buildings including timber with at least six stories was increased from 32 in 2015 to 115 in 2023.

Even though the number of timber buildings is increasing, the actual environmental impact is largely unknown. This is because there is no commonly-used method to calculate the carbon footprint of a building which is complete and correct. Currently, the MPG (MilieuPrestatie Gebouwen) and the method described in the Paris Proof Agreement are mainly used in the Netherlands. The MPG uses the Environmental Product Declarations (EPDs) from the database from the NMD viewer, but this viewer does not provide the essential information for the user to choose the proper EPD. The Paris Proof Agreement disregards the end-of-life phases, which leads to incomplete results. Therefore, another method was developed to calculate the carbon footprint and to determine the difference in carbon footprint between a concrete and/or steel structure with a timber-hybrid structure. This method uses two sets of phases: phases A-C and phases A1-A5. The former uses all relevant LCA phases and will provide the most accurate results, while the latter can be used to compare the results to the Paris Proof Agreement limits. Phases A4 and C2 (transport to and from the building site) and modified to fit the current projects.

Two case studies were used for this research. The first case study is KasseNova aan de Vaart, a seven-story residential building made of concrete. The carbon footprint is calculated for this concrete design, as well as three design variants including CLT floors, CLT walls and a combination of the two. The second case study is Apollolaan 171, a six-storey office building made of steel and concrete. The design variants include glulam columns, CLT floors and beams and a combination. For all variants, design calculations of the timber elements were performed. For CLT elements, two end-of-life scenarios were considered: 100% recycling and 100% incineration. The current design of KasseNova aan de Vaart has a carbon footprint of 3,145 ton CO2-eq. when phases A-C are considered. In the scenario that the floors and walls are replaced by CLT, the carbon footprint is decreased by 63.1% when the CLT is recycled, while this is decrease is 12.7% when the CLT is incinerated. When phases A1-A5 are considered, the current design has a carbon footprint of 222.46 kg CO2-eq./m² (above the 2021 Paris Proof limit of 220 kg/m2) and the CLT floor and wall design variant has a carbon footprint of 35.12 kg CO2-eq./m² (below the 2050 limit of 50 kg/m2), including biogenic carbon uptake. The current design of Apollolaan 171 has a carbon footprint of 1,671 ton CO2-eq. (phases A-C). For the scenario in which the floors, beams and columns are replaced by CLT and glulam, the carbon footprint is reduced by 89.2% (CLT recycled) and 49.8% (CLT incinerated). Considering phases A1-A5, the carbon footprint of the current structure is 255.17 kg CO2-eq./m2 (above the 2021 limit of 250 kg/m²), while the carbon footprint of the structure including CLT and glulam elements is -44.93 kg CO2-eq./m² (below the 2050 of 50 kg/m²).

These results show that an increase in timber in the structure leads to a reduction in carbon footprint. This is because timber takes up carbon in the product stage. However, the amount of reduction depends on several factors. If the CLT is recycled at the end of its lifetime, the reduction will be more significant than if the CLT is incinerated. When the structure includes concrete, the carbon footprint depends on the type of cement being used in the concrete. CEM I will lead to a higher carbon footprint than CEM III. For structures including steel, a higher percentage of recycled steel leads to a lower carbon footprint. Also, in general, the country of production influences the carbon footprint. If a country has a high percentage of coal in its energy mix, the carbon footprint will be higher.

Currently, most of the modular building can be fabricated off-site, except for the stability system. Therefore, the question arises: Could modules be designed such that there is no need for an additional stability system? As modules are typically built in a rectangular shape, incorporating stability elements such as bracings along the longer side of the module is not the problem. The main challenge lies in the limited length available for stability elements on the shorter side of the module, combined with the fact that this shorter side is commonly used for windows and openings for door frames. This introduces a conflicting interest between structural capacity and daylight within the module. This conflicting interest becomes more and more prominent as the building height goes up. A possible solution to this problem can be found in the use of a load-bearing window frame with glass infill as a stability element, often referred to in literature as a timber-glass shear wall (TGSW).

Therefore, this thesis will answer the main research question: 'To what extent can the structural performance of a timber-glass shear wall as a stability element in a timber module be used to accommodate for the stability of a mid-rise modular timber building?'

The approach to answering the main research question consists of several steps. First, a literature study was conducted on modular buildings and TGSW's. The outcome of the study has provided insight into how modular buildings are constructed in general and how relevant aspects such as progressive collapse, fire safety design, and foundation design influence structural design. The study also resulted in an analytical prediction model for the load-bearing capacity and stiffness of the TGSW. Through this prediction model, it became clear how the properties of individual components relate to the load-bearing capacity and stiffness of the total TGSW-system.

The second step was to propose a design for a modular timber building composed of timber modules. To save on computational time, the stability elements of the building are modelled using steel diagonals as an equivalent system for the TGSW. The cross-sectional area of the steel diagonals is directly related to the properties of the TGSW. Therefore, the steel diagonals have identical stability properties as the TGSW. In this study, varying the type of adhesive and the spacing of the screws was found to have the most significant impact on the overall structural properties of the TGSW. The horizontal connections are made of steel plates fastened with screws. The vertical connections are realised by shear plate connectors. The entire building was modelled in a 3D FEM programme to assess the structural behaviour of the building and its compliance with building regulations. Several building configurations ranging from 1:1 to 1:3 height-to-width ratio were investigated. For each building configuration, the cross-sectional area of the steel diagonals was adjusted within a specified range. This range corresponds to variations in adhesive type or screw spacing. As a result, design graphs were produced, which present the requirements for the load-bearing capacity and stiffness of the stability system. These can be compared to the load-bearing capacity and stiffness of the TGSW. This comparison can be used as a validation method to determine the viability of the TGSW stability element in a modular building.

The results of this study indicate that a modular building can be stabilised by a TGSW up to six stories within the height-to-width ratio of 1:1 to 1:3. The minimum building configurations per story height are: 3 modules high by 5 modules wide, 4 by 8 modules, 5 by 12 modules, and 6 by 18 modules. These slenderness ratios were governed by the strength of the TGSW. The limiting factor in the load-bearing capacity is the shear strength of the adhesive. These slenderness ratios could only be reached with elastic adhesives such as silicones.

The next step is to create a more extensive FEM model that could predict the load-bearing capacity and stiffness of the TGSW in a more accurate way compared to an analytical model. Furthermore, exploring the performance of the TGSW under different horizontal loads, such as earthquakes, would give valuable insight.

To address the increasing housing demand in Europe and simultaneously tackle the challenge of creating a more sustainable construction industry, timber modular buildings present an innovative solution. However, before multi-storey modular buildings become a widespread practice, various engineering challenges need to be addressed. Ensuring robustness is one such challenge. This study focuses on the robustness of post-and-beam timber modular buildings, particularly through catenary action. The challenge with ensuring robust catenary action lies in designing connections with sufficient resistance and deformation capacity. This study proposes an optimisation process to determine the required mechanical properties of inter-module connections to enable robustness through catenary action.

The principle of a catenary relies on the equilibrium between a vertical point load and the vertical component of the tie force in the deflected floor elements. Larger deflections result in a lower required tension resistance but demand a larger deformation capacity in the components. This study introduces a catenary equation to determine the required tensile resistance in a catenary at a specified elongation, creating a catenary requirement boundary. For a timber modular building to form robust catenary action, the axial force-elongation response in a catenary must meet this boundary. The catenary equation and the force-elongation response of the catenary form the basis of the connection optimisation, as the inter-module connection governs the response.

To determine the optimised mechanical properties of an inter-module connection in a timber modular building, a case study was performed on a building consisting of twelve post-and-beam modules in width and five modules in height. To determine the effect of a change in the inter-module connection design on the force-elongation response of the buildings, quasi-static numerical analyses were conducted on 2D models, focussing on the frontal view frame of the building, and the floor plane. The load distribution through the floor system and corresponding deformation were added to the frame model by use of spring boundary constraints, after which the catenary could be examined.

As a catenary can be formed by increasing the axial resistance, or its ductility, two optimisation methods were formulated, resulting in a high-strength inter-module connection and a ductile inter-module connection with a fuse. The optimisation process is based on iterations of the inter-module connection design. The resulting high-strength connection required a 143% increase in tension resistance, while the ductile connection relied on a 55% increase in resistance and a 550 mm fuse.

This study underscores the complexity and critical importance of correct connection design to ensure structural robustness, emphasising the need for sufficient strength and deformation capacity. While the proposed methodology serves as a valuable tool for optimising connections in timber modular buildings, further research is recommended by including dynamic analyses in the optimisation process and experimental testing of inter-module connections to enhance the accuracy of the models.

The construction industry contributes significantly to global emissions. In response to the growing concern about climate change, new methods are being developed to reduce these emissions. Building with timber is one such approach, as it can be CO2 neutral if reforestation is practiced. Timber is a lightweight and flexible material compared to traditional construction materials like steel and concrete, which can result in high accelerations and deflections, negatively affecting user comfort. Engineered wood products such as CLT and GLT make it possible to construct larger panel sizes and spans, which can lead to more efficient building design. Many buildings utilize core systems to provide lateral stability and facilitate vertical transportation of goods and people. Therefore, replacing a conventional concrete core with a CLT core could be a viable solution to reduce the building’s environmental impact. Timber, being a flexible material, often lacks the necessary stability to meet user requirements for deflection and acceleration in high-rise buildings. An outrigger, similar to those used in concrete and steel structures, can provide the solution to enhance user comfort. The outrigger transfers bending moments from the core to the columns, reducing forces in the core and increasing overall stiffness. However it is unclear what the influence of the addition of a timber outrigger on a CLT core building is and how such a system can be improved. Therefore the purpose of this thesis is to evaluate the impact of a timber outrigger on a CLT core building, and provide guidance for structural engineers on how to improve the structural behaviour of such a system. The impact of adding an outrigger is evaluated through the comparison of different numerical case studies with and without timber outriggers. Additionally a sensitivity analysis is performed in which the influence of core joint design and the impact of outrigger design parameters is evaluated. By introducing a timber outrigger to a CLT core building bending moments are transferred from the core to the column, partially restricting rotation of the core. This will have the following effects on the behaviour of the structure. Firstly, the deflections due to lateral wind loading are reduced due to the increased global stiffness. Secondly, the increased stiffness of the structure will result in a reduction of peak lateral acceleration. Thirdly, by transferring loads from the core to the columns the strength requirements on the connections of the core are reduced. Finally, by introducing a timber outrigger system to a CLT core building horizontal forces are generated in the core at outrigger level, which should be accounted for in the design phase of the vertical core joints. Increasing the stiffness of the outrigger will further reduce deflections, peak lateral acceleration and strength requirements on the core joint, however strength requirements on the vertical core joints at outrigger level will further increase. An exponential relationship has been derived between the lateral deflections and the ratio between the effective bending stiffness of the outrigger and the effective bending stiffness of the core, a similar exponential relationship has been derived for the peak lateral accelerations Additionally it was investigated what the critical design parameters are and how the performance of a CLT core building with timber outriggers can be improved. For the design of a CLT core the connection between the core and foundation showed to be critical, having large effects on the lateral deformation. While increasing the stiffness of the vertical connections showed to have little influence on the interaction between core walls due to their respective high interaction factors. In the design of the outrigger it was shown that a two storey outrigger is able to more than double the reduction in deflections compared to a single storey outrigger, further increasing the overall effectiveness of the system. Finally the effectiveness of the system was found to be significantly influenced by the configuration of the outrigger truss, demonstrating a greater impact than increasing member size or connection stiffness.

The importance of joints in timber structures is strongly emphasized in the existing literature (e.g., Blaß & Sandhaas, 2017; McLain, 1998). The aim of this project is to provide insight into whether the cross-sectional sizes of the member are dictated by the dimensional sizes of the laterally loaded dowel-type connection or the strength and stiffness requirements of the member itself in timber frame structures.

In this research project, a parametric study is performed. The parameters in this study represent the global frame structure and the laterally loaded dowel-type connections. Together, these parameters form a parametric model that lays the foundation for the tool that is constructed in this study. This tool is built in order to generate a number of unique configurations that fulfill the design verifications. Using the tool, two analyses are performed. In analysis 1, the effect of different distances between the secondary beams is examined. In analysis 2, the effect of different grid sizes of the column in the frame structure is studied. In both analyses, two member sizes are first selected based on the criteria 'lowest cross-sectional area' (LCA) and 'lowest height beam' (LHB). These two member sizes form the starting point for generating different configurations of laterally loaded dowel-type connections.

In this research project, three factors are found to contribute to the largest reduction in the number of unique configurations for all constructed cases examined in analysis 1 and 2. These three factors are small column widths combined with high shear forces, the effect of a 'compact' member, and the effect of 'brittle' failure mechanisms on the LCA-members, which was selected as a design constraint in this study. These factors may be relevant for engineers to take into account when designing the structural members.

However, in this study, no constructed case is found in which the member needs to be redesigned in order to fit the connection. This means that one can conclude that the dimensional size of the structural member is dictated by the strength and stiffness requirements of the member itself. Important to note is that, although a large number of parameters was incorporated into this study, not all potentially relevant parameters were taken into account. When incorporating factors such as the horizontal forces in the connection, the effect of shrinkage and swelling, the level of difficultly in terms of assembling the joints on site, and adjustments to guarantee a certain level of fire resistance, certain turning points in the dimensional interaction between joints and members may be found.

Finally, beyond allowing for the dimensional interaction between joints and members to be studied, the tool constructed in this study is also valuable to practical engineering. The large amount of data that is generated by the tool allows the engineer to explore the different possible configurations in the process of designing joints. By connecting the output of the tool to the Design Explorer interface, the engineer has the opportunity to search through all the individual characteristics or a specific range and examine different possible connections in an efficient manner. One of the main contributions of this research project, therefore, lies in the tool itself.

Dynamic behaviour often is a topic of concern in the design of pedestrian bridges. It is time-consuming to assess and little is known about the way it is influenced by the characteristics of a bridge. In many cases, a bridge needs testing after is has been finished to determine the specifications of a damper.

Striving to reduce the environmental impact of bridges, there lies a great potential in using materials with a low environmental impact, such as timber. This research combines the lack of knowledge about dynamic behaviour of footbridges with the need for using timber instead of other materials. It consists of two parts. The first part, the parameter study, investigates the influence of three preliminary design parameters on the dynamic behaviour of a long-span timber footbridge, namely the pylon height, the pylon shape and the amount of cables. The second part, the optimisation study, examines to what extent it is possible to design a long-span timber footbridge that does not need dampers to control excessive vibrations.


To this end, a parametric model of a bridge was made in which parameters can be varied and optimised to create realistic design variants. To be able to optimise taking into account dynamic behaviour, a python script was written to automatically determine the type of modes. The results of the parameter study show that the dynamic behaviour can be influenced by the parameters, although the results depend on the specific model, dimensions, parameter values and damping value. The results of the second part show that a with a 14% increase in mass a design variant that does not need dampers to control excessive vibrations can be obtained.

Low-frequency sound transmission in a cross-laminated timber apartment building can result in annoyance, even if the acoustic requirements of the building code are fulfilled. Cross-laminated timber is an upcoming material in the building industry. But there are also problems arising when building with this relatively new material. CLT is a lightweight building material, which means that the mass itself is insufficient for meeting the acoustical requirements. The total sound transmission depends on the amount of direct sound and flanking sound transmission. The ISO 12354 standard used to determine the amount of sound transmission between rooms does not include frequencies below 100 Hz. Even though these low-frequency sounds are the main cause of annoyance in lightweight construction buildings. The low-frequency sound transmission is hard to measure because of the long wavelength. In this research, a numerical model was developed and used to determine the low-frequency sound transmission in CLT apartment buildings.


The effect of the following sound-reducing measures are studied: the material properties of the material CLT, additional linings on the room separating elements, use of elastic interlayers between CLT panels and the type and number of connectors connecting the CLT panels. These are all common sound-reducing measures for lightweight constructions. The effect of the material properties of the CLT and the effect of additional linings are computed by a numerical direct sound transmission model. The effects of elastic interlayer and connectors between the CLT panels are computed with a numerical vibration reduction index model. The results of the numerical models are compared to measurements found in literature and the sound transmission according to the ISO standard.

The results showed the importance of Young’s modulus in the y and z-direction, these influence the location of the resonance induced dips in the sound insulation. The internal loss factor of the CLT panels influenced the height of the dips. A loss factor of 20 % resulted in results most similar to the measurements. The direct sound transmission through a bare CLT panel can be predicted within a range of 3 dB difference with measurements. The prediction of the ISO standard is within a range of 5 dB with the measured values.

The vibration reduction index between panels without interlayers is modelled with frictional contact regions between the panels. The numerical results showed similarities with the measurement results for the vibration reduction index of panels with screwed connectors. The ISO standard significantly overpredicts the vibration reduction index of CLT junctions. The effect of the elastic interlayer showed insignificant improvements in the frequency range 50-500 Hz, the additional reduction stays below 3 dB. The ISO standard does not include a method to determine the effect of elastic interlayers or connectors between CLT panels.


The numerical models prove that is possible to predict the low-frequency sound transmission in CLT apartments. Important notes are that the CLT lamellas need to be modelled separately. Only in this way the model is able to capture the sound that goes through a structure within a range of 3 dB. In order to test the effect of additional lining, the material properties need to be known.
The vibration transmission between panels in the junctions is more complex, as it depends on more design parameters. A frictionally bonded contact region between the panels results in vibration reduction indices that are in line with measurement results of panels with several connectors. The effect of the elastic interlayer is minimal in the low-frequency range, but the results are similar to measurement results. Both the direct sound transmission model and the vibration reduction model were influenced by the boundary conditions.

Increasing housing demand in Europe and the need to be more sustainable are asking the construction industry to leave the traditional pathways and innovate. An emerging construction method with volumetric timber modules potentially offers the solution. However little is known about the robustness of this new innovation. Therefore, this thesis aims to advance the current research regarding collapse resistance in volumetric modular timber buildings. To achieve that goal, first, in this thesis, a literature study into robustness and modular buildings was performed. The study identified the importance of redundancy, proper connection design, ductility, and tying in modular structures for robustness. Secondly a case study was performed. The case study provided the structural design concept of a newly developed volumetric timber post and beam module by Lister Buildings, structurally designed by Pieters Bouwtechniek. The modules consist of glued laminated beams and columns with cross-laminated floor and ceiling slabs. With the modules, a hypothetical residential building of 5 storeys was created, which consecutively was decomposed into equivalent two-dimensional frame structures suited for 2D finite element analysis. To account for the mechanical behaviour of the connections in the models, nonlinear springs were used. To establish the springs, the component method was adopted. The spring behaviour was determined from the elastic, plastic and failure performance of the individual components of a connection in translational and rotational degrees of freedom. Then based on a notional element removal concept, multiple possible loss events of load bearing elements were analysed in the finite element software of Abaqus to examine the existence and development of alternative load paths. To do that, both nonlinear static and nonlinear dynamic analyses were performed. The results of this study indicate that the new design concept performs quite well on robustness. Several alternative load paths were identified, among which cantilever action, bridging action, and catenary action, depending on the removal event and scenario. In addition this thesis investigated the dynamic amplification factor (DAF) of the modular system. The results of this research imply that for alternative load path analysis of timber structures, a DAF of 2.0 should be applied in a (non)linear static analysis. More research will be necessary to examine whether a lower value than 2.0 can be used.